The basement at the Science Museum is great for kids. Experiments and puzzles that make up a world of edutainment.
Exhibition Road, SW7; Tel: 0870 870 4868; Tube: South Kensington; www.sciencemuseum.org.uk/
Updates
If it is very busy, try the top floor of the Earth Galleries for the Kobe earthquake simulation. If that fails, walk up Exhibition Road to Hyde Park and then over to the Princess of Wales playground with pirate ship and cafe for tired parents.
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